[1967Tempest]

Is total cubic inches just what is available in the block? It was never explained to me why head CC isn't part of the engines total cubic displacement.

Or maybe it was and I forgot.

Thanks in advance...

[goatless]

The engine displacement is the total of the air displaced by the pistons as they move up and down.

[AG]

Cubic inches refers to the cubic inch displacement of a motor which is the swept volume of one piston times 8. The swept volume of one piston is the volume of a cylinder, or the diameter squared times pi times the stroke all divided by 4.

[Garry Sr]

The wrath of math.... Sure I could have run domed pistons but flat tops seem to go very well with the new E-Head combustion chamber design.

[Garry Sr]

You can harp on cast iron until the cows come home but the factory never offered anything like these.

[b-man]

It's all about bore size, stroke length and the number of cylinders.

Nothing else.

[george kujanski]

I understand the question and it sounds like it's just the convention used. Mathematically I agree that the chamber volume should be added to the cylinder volume....but then again if a dished piston is used, that needs to be taken into account also........

George

[74Grandville]

Double post

[Schurkey]

This thread has posts in it that don't make a bit of sense to me in the context of chamber volume vs. displacement. Have there been posts deleted that removed the context for some of the remaining posts???

Originally Posted by george kujanski

Mathematically I agree that the chamber volume should be added to the cylinder volume....

To determine engine CID? No. The chamber volume in the head is unchanging. Chamber volume affects compression ratio in nearly all engines, but it doesn't change displacement.

Originally Posted by george kujanski

but then again if a dished piston is used, that needs to be taken into account also.

To determine engine CID? No, it doesn't. The configuration of the top of the piston means nothing to CID, although it can radically alter compression ratio.

If you consider a single-cylinder engine as a positive-displacement pump, the motion of the piston from TDC to BDC at low speed with intake valve open, will draw in a certain amount of air. I say "at low speed" because we don't want to clutter the measurement with ram-air principles or port restriction, and we don't need to be so picky as to account for piston rock in the bore. You could measure the volume of that single cylinder's worth of air any number of ways, but in the end, it's going to amount to "pie are squared" times stroke. Piston dome or dish will have no effect.

In essence, it's the amount the volume of the cylinder changes as the piston goes down--or back up. The volume of the head + gasket, or the volume of the piston dish or dome, is meaningless as it doesn't affect the change of volume due to piston motion. The chamber volume, and piston dish/dome affects the RATIO of minimum vs. maximum volume for that cylinder--the compression ratio.

[JLMounce]

Originally Posted by Schurkey

This thread has posts in it that don't make a bit of sense to me in the context of chamber volume vs. displacement. Have there been posts deleted that removed the context for some of the remaining posts???


To determine engine CID? No. The chamber volume in the head is unchanging. Chamber volume affects compression ratio in nearly all engines, but it doesn't change displacement.

To determine engine CID? No, it doesn't. The configuration of the top of the piston means nothing to CID, although it can radically alter compression ratio.

If you consider a single-cylinder engine as a positive-displacement pump, the motion of the piston from TDC to BDC at low speed with intake valve open, will draw in a certain amount of air. I say "at low speed" because we don't want to clutter the measurement with ram-air principles or port restriction, and we don't need to be so picky as to account for piston rock in the bore. You could measure the volume of that single cylinder's worth of air any number of ways, but in the end, it's going to amount to "pie are squared" times stroke. Piston dome or dish will have no effect.

In essence, it's the amount the volume of the cylinder changes as the piston goes down--or back up. The volume of the head + gasket, or the volume of the piston dish or dome, is meaningless as it doesn't affect the change of volume due to piston motion. The chamber volume, and piston dish/dome affects the RATIO of minimum vs. maximum volume for that cylinder--the compression ratio.

bold and red. You don't measure the combustion chamber because the volume doesn't change.

[craigs69]

Excellent explanation Schurkey!

[george kujanski]

Sorry, in my mind I was thinking calculating the CR......

George

[Tom Vaught]

Originally Posted by craigs69

Excellent explanation Schurkey!

X2!

Tom V.

I see posts on other engine theory websites where the presenter says "If you think that Rod Length changes the stroke, stop right here and go to a different website." How are you going to ever get the right answer if you never ask the question? An answer like that is a BS answer and does not help the person asking the question at all. Again good job one and all.

[tempest1964]

Originally Posted by AG

The swept volume of one piston is the volume of a cylinder, or the diameter squared times pi times the stroke all divided by 4.

I went to college and came home the first summer. Daddy said "Boy, what did you learn at this school"? I said I took a math class and learned Pi R square. He said "Damn boy, what a waste of money. Everybody knows pie are round, corn bread are square"!

[AG]

Originally Posted by tempest1964

I went to college and came home the first summer. Daddy said "Boy, what did you learn at this school"? I said I took a math class and learned Pi R square. He said "Damn boy, what a waste of money. Everybody knows pie are round, corn bread are square"!

Good thing you learned something!

[Schurkey]

Originally Posted by tempest1964

I went to college and came home the first summer. Daddy said "Boy, what did you learn at this school"? I said I took a math class and learned Pi R square. He said "Damn boy, what a waste of money. Everybody knows pie are round, corn bread are square"!

Three squaws were each preparing for the birth of their first child. The
first squaw placed a large bear hide by a river, the second squaw placed
an elk hide by a tree by a river, and the third squaw placed a
hippopotamus hide by a path, near the river and the tree so that the
three formed a triangle.
It just so happens that all three women gave birth on the same day.
The first squaw on the bear hide had a 5-lb son, the second squaw on the
elk hide had a 6-lb son, and the third squaw on the hippopotamus hide had
an 11-lb son.
To this day, mathematicians credit these three women with the first
proof of the Pythagorean Theorem:
"The son of the squaw of the hippopotamus is equal to the sons
of the squaws of the two adjacent hides."

The cornbread, and the squaws were my big take-away from Junior Hi math.

[Garry Sr]

I got a new one from watching Andy Griffith today.... "Hooked like a starving catfish"

[johnta1]

Hmmm...

the hippo of 5 and 6 should be 7.81 lbs?



I learned about square pies in about 5th grade?

["QUICK-SILVER"]

Originally Posted by johnta1

Hmmm...

the hippo of 5 and 6 should be 7.81 lbs?

Shurk didn't mention the tree being abnormal/deformed.
It must of had square roots!

[Garry Sr]

One more for you guys.... "Gone like two hound dogs that backed into a porcupine"

I'm check out now.